The present invention relates to waste water treatment, and more particularly to a nocardia foaming controlling method of waste water treatment which is a solution to the nocardia foaming problems by controlling nocardia foaming.
Nocardia spp. is a branched filamentous microorganisms that produce a brown, viscous foam in many activated sludge plants. Due to the tenacious nature of the foam, serious problems can develop as foam accumulates. Slippery walkings and odors result when foam overflows aeration basin walls. Foam flowing over or under clarifier baffles increases effluent suspended solids and can freeze on clarifiers during cold weather that deteriorate the effluent quality and disrupt the treatment process. In addition, waste sludge containing Nocardia can cause serious foaming in anaerobic digesters.
Nocardia occurs in many different types of water pollution control plants with a variety of influent characteristics. Surveys performed by a number of researchers have found that Nocardia is one of the most commonly observed filamentous organisms in activated sludge plants in the United States. Though the causes of nocardia growth are not very well defined, it is commonly associated with long solids retention time, warmer temperatures, and grease, oil and fat present in the influent.
Existing nocardia control methods may be successful in alleviating some of the symptoms, but generally, there are no quick solutions and high foaming levels can linger for months. Furthermore some suggested methods for foam control can results in inadequate treatment, and deteriorated effluent quality. Chemical anti-foaming agents can be used to restrain foaming, but there are not effective as a long term solution. Disinfectants are also not successful because the amount often required to have an impact on nocardia can have adverse effects on the biological treatment either by resulting in floc dispersion or by limiting floc forming microorganisms.
Operational changes also have limited effect on nocardia and sometimes can have detrimental effects on the treatment process. Reducing aeration rates, or SRT can deteriorate effluent quality. Recent attempts involve using selectors at the head end of aeration basins, however this option can require significant capital modifications, and there effectiveness is not consistent for each plant. Other techniques, also of varying levels of success, include, the use of water spray, digester subnatent, and selective foam wasting.
Conventional sludge treatment process consists of bar screening, aerated grit removal, primary sedimentation, and activated sludge biological treatment. The sludge is anaerobically digested, dewatered and hauled for land applications. FIG. 1 is a schematic view of the conventional sludge treatment.
The biological aeration consists of none basins, which are generally operated in a serpentine flown pattern, with three tanks in each serpentine. The secondary treatment is characterized by the high ratio of recirculation (0.8) and the anoxic regions created to act as a selector for filamentous control. The flow outlets from the aeration basins are submerged, as well as gates between the basins themselves. The basins ate equipped with defoaming spraying equipment.
The conventional sludge treatment has long standing nocardia problems due to the industrial discharges it receives, especially from refineries and food processing facilities, and also due to the long sludge retention time (SRT). There have been incidents where excessive foaming has overflown the aeration basins creating slippery conditions on the walkways. Once nocardia has been established in the system control options have had limited success. Because of the hydrophobic nature of nocardia they float at the top of aeration basins and thus they are often trapped in the basins due to the design of the outlet.
Nevertheless, intensive research on this organism has, thus far, not yielded a control method that can be easily implemented in water pollution control plants.